Yoke apparatus for rack and pinion

ABSTRACT

A yoke assembly for a rack and pinion steering system includes a bearing disc member having a pair of bearing surfaces for slidingly supporting and urging the rack toward the pinion. The bearing disc member is kinematically supported by an elastomeric member along an adjustment axis. The elastomeric forces are conically applied toward an apex located well within the rack and away from the bearing surfaces. This results in the bearing disc member rotating slightly in a contra-pitch direction and forming a lubrication wedge whenever the rack moves along its axis of translation. In addition, elastomeric means for compliantly biasing the bearing disc in a lateral direction orthogonal to a plane defined by the adjustment and translation axes toward a preferred central location are disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention is a continuation-in-part of U.S. Ser. No.08/630,369 filed Apr. 10, 1996 and entitled "YOKE APPARATUS FOR RACK ANDPINION.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention is directed to a yoke apparatus for use with arack-and-pinion steering system.

II. Description of the Prior Art

Automotive steering systems typically include a housing having a rackdriven by a pinion gear. Rotation of a steering wheel turns the piniongear. The pinion gear meshes with a plurality of teeth formed on therack to drive the rack in one of two reciprocal directions. The rack inturn is connected to a pair of dirigible wheels. In addition, manyautomobile steering systems comprise a rotary control valve which isoperable to supply pressurized fluid to move a double-acting hydrauliccylinder or actuator to assist translation of the rack.

In order to keep the teeth of the pinion gear and the rack inengagement, such steering systems employ a yoke apparatus. The yokeapparatus includes a bearing member which is biased to force the racktowards the pinion gear. The bearing member has a pair of spaced apartbearing surfaces which slidingly contact the surface of the rackopposite the teeth of the rack. The bearing member is slidingly mountedin a bore which is formed in a nominally orthogonal manner withreference to the rack's intended position. This results in a nominalalignment of the bearing surfaces along an axis which extends coaxiallywith the axis of translation of the rack. A spring is mounted in thebore to force the yoke assembly against the rack and bias the bearingsurfaces in order to force the teeth of the rack against the teeth ofthe pinion gear. Thus, the yoke apparatus operates to nominally guidethe rack along the axis of translation and hold the teeth of the rackand the teeth of the pinion gear in mesh during the application oftorque to the pinion gear.

In practice, it is not possible to maintain the axis of translation ofthe rack orthogonal to the axis of the bore. This is because of thetolerances involved in forming the bore, rack, and pinion gear.Accordingly, it has been found that the axis of translation of the rackmay be angled with respect to the axis of the bearing surfaces of thebearing member, and may even undulate as a function of rotational motionof the pinion gear. When so missaligned, one end of each of the supportsurfaces engage the rack while opposite ends of the support surfaces arespaced away from the rack. As a further result, the bearing memberitself may suffer angular misalignment within the bore and jam. In fact,such yoke assemblies may be said to be over constrained or to be ofnon-kinematic design.

For the above reasons, the rack is often held from smooth movement inone, or both, directions of travel. This is particularly so when therack travels in a direction from the contacting ends towards thenon-contacting ends of the support surface. The edges resist movement ofthe rack and the rack tends to hesitate and jerk in its movement.However, movement of the rack in an opposite direction tends to producea smoother, less resistant movement. Frequently, the discontinuous orhalting movement of the rack will be tactilly sensed by the driver.

The spring is located in an adjuster plug which is threadably insertedin the outer portion of the bore. During the assembly of the yokeapparatus, the adjuster plug is rotatably driven into contact with thebearing member with a nominal torque value of perhaps 50 in.lbs. toprovide a rotational position reference. Because of the above notedtolerances involved in forming the bore, rack and pinion gear, thereresults a soft contact between the adjuster plug and the bearing member,and thus an imprecise rotational position reference. For this reason,the adjuster plug must then be backed off by an angle of about 30° inorder to ensure interference free operation in the manner describedabove. This results in an indefinite stop position of the bearing membershould a torque level be applied that is sufficient to overcome thespring bias.

In operation, rack and pinion assemblies are often subject to acondition known as "rattle". Rattle most often occurs when the dirigiblewheels are subject to dissimilar impacts such as when crossing obliquelydisposed railroad tracks or similar road surface discontinuities. It hasbeen found that lateral and rotational motions and resulting impactswithin the housing by the yoke apparatus elements are the mostsignificant cause of rattle. This occurs because of the helically formedteeth on the pinion gear. As the pinion gear is caused to rotate byaxial thrust loads imposed upon the rack with resulting axial motionthereof, the rack is driven laterally by the helically formed teeth ofthe pinion gear. In addition, physical separation followed by abruptre-engagement of the rack and pinion gear interface as a consequence ofthe axial thrust loads contributes some rattle as well. In any case,rattle is typically treated by tightening up various clearances oradding a circumferential elastomeric guide element around the skirt ofthe yoke, and as a last resort, by significantly increasing the biasingspring force.

SUMMARY OF THE INVENTION

Accordingly, a primary object of the present invention is to provide ayoke apparatus having a true kinematic design wherein bearing surfacesare maintained in coaxial alignment with the axis of movement of therack to provide smooth, constants movement of the rack in bothdirections of travel. Another object of the present invention is toprovide a yoke apparatus enabling substantially rattle free operation ofthe rack and pinion assembly.

Accordingly, in a preferred embodiment of the present invention, animproved first yoke apparatus is presented wherein a bearing disc isbiased to force the rack towards the pinion gear by an elastomericO-ring member. The bearing disc is nominally constrained in the lateraldirections with reference to a supporting adjuster plug by the O-ringmember. This is accomplished by compressing the O-ring member betweeninner and outer angular contact grooves respectively formed on thebearing disc and adjuster plug, respectively. The adjuster plug is usedto axially compress the O-ring member in order to provide the biasingforce. Because of the compliant nature of the O-ring member, the abovedescribed over constraint is eliminated.

As a consequence of its axially directed compression, the O-ring memberprovides nominal pitch and yaw constraints upon the bearing disc whichare conically directed toward an apex. The actual location of the apexis determined by the relative final locations of the lines of forcethrough the angular contact grooves. In any case, the pitch constraintis directed about the apex which is located well within the rack andthus physically remote from the bearing disc. Upon initial translationof the rack, the bearing disc begins to move along with the rack. Thistends to decompress the portion of the O-ring member under the leadingedge of the bearing disc and further compress the portion of the O-ringmember under the trailing edge of the bearing disc. The end result is acontra-pitch rotation of the bearing disc about the apex so as to form alubrication wedge between it and the rack. Thus, the bearing surfaces ofthe bearing disc can compliantly align with the preferred axis ofmovement of the rack in a manner that provides enhanced lubrication.

In practice it has been found that while the improved yoke assembly ofthe preferred embodiment does provide for smooth, rattle-free movementof the rack, the helically formed teeth on the pinion gear tend toinitially drive the rack laterally. This, in turn, may cause the hostrack and pinion assembly to exhibit a lack of on-center crispness. Thisis due to a lack of initial translational motion of the rack during theperiod when it is moving laterally.

Therefore, in a first alternative preferred embodiment of the presentinvention, an improved second yoke apparatus is presented whereinlaterally disposed elastomeric members are utilized to markedly increaseyaw stiffness of the bearing disc. The laterally disposed elastomericmembers are captured between grooves formed in sides of the bearing disclocated outwardly from its bearing surfaces, and juxtaposed nominallyaxially directed grooves formed within the bore. In order to easeassembly, the lateral grooves formed in the bearing disc compriselead-in tapers so that compression of the laterally disposed elastomericmembers occurs gradually as a function of the axial assembly of thebearing disc.

In the improved second yoke apparatus, the O-ring described above (i.e.,with reference to the preferred embodiment) is replaced with anelastomeric member formed directly within the adjuster plug. Thiseliminates handling a separate elastomeric member during assembly. Inthis case, the elastomeric member is formed within an outer angularcontact region such that the resulting force direction is similar tothat of the preferred embodiment.

In a second alternative preferred embodiment of the present invention,an improved third yoke apparatus is presented wherein both of the abovedescribed types of elastomeric members are formed in a second operationdirectly within the bearing disc. Because it is difficult to bondelastomeric materials to materials which are suitable for forming thebearing disc, the bearing disc is formed with mechanically interlockingfeatures for the elastomeric members. So forming the elastomeric memberseliminates handling separate elastomeric members during assembly. And inthis case, no grooves are required within the bore. The bore is simplyformed in a conical manner as will be described below.

In either of the first or second alternative preferred embodiments ofthe present invention, the laterally disposed elastomeric membersprovide a substantial increase in yaw stiffness for the bearing disc.Thus, the helically formed teeth on the pinion gear are substantiallyprecluded from driving the rack laterally. This, in turn, substantiallyenhances on-center crispness.

In any of the preferred embodiments of the present invention, all of thenecessary constraints are elastomerically provided. Thus, the bearingdisc is not required to be slidingly mounted in a bore in the housing.And, there is no possibility of rattle occurring via contact between thebearing disc and such a bore. In addition, because all of theconstraints are elastomerically provided, engagement of the teeth of thepinion gear and the rack is maintained in a less abrupt manner. Shouldphysical separation therebetween result from a dissimilar impact,re-engagement is softer and somewhat damped. In this way, rattle due togear re-engagement is minimized as well.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and advantages of the present inventionwill become readily apparent to those skilled in the art upon studyingthe following detailed description, when considered in connection withthe accompanying drawings, in which:

FIG. 1 is an exploded perspective view of a steering gear assemblyincluding a yoke apparatus configured in accordance with a preferredembodiment of the invention;

FIG. 2 is a sectional view of the yoke apparatus of the preferredembodiment of the invention;

FIG. 3 is a sectional side view of the yoke apparatus of the preferredembodiment of the invention;

FIG. 4 is a sectional view of a yoke apparatus configured in accordancewith a first alternative preferred embodiment of the invention;

FIG. 5 is a sectional side view of the yoke apparatus of the firstalternative preferred embodiment of the invention;

FIG. 6 is a sectional view of a yoke apparatus configured in accordancewith a second alternative preferred embodiment of the invention;

FIG. 7 is a sectional side view of the yoke apparatus of the secondalternative preferred embodiment of the invention; and

FIG. 8 is an isometric view of a bearing disc used in the secondalternative preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the exploded perspective view of FIG. 1, thereshown isa portion of a steering apparatus for a vehicle. The steering apparatusincludes a conventional housing 10, such as manufactured by the SaginawSteering Systems Division of Delphi Automotive Systems, of Saginaw,Mich. The housing includes a barrel 12 extending upwardly from acylinder 14. The barrel 12 houses a rotary control valve assembly 18 forproviding pressurized hydraulic fluid through ports 16 to a hydraulicactuator (not shown) for providing hydraulic assist to the steeringsystem. Included in the rotary control valve assembly 18 is a piniongear 20.

The pinion gear 20 comprises helically formed teeth 28 and is mounted ata non-orthogonal angle in order to mesh with a plurality of teeth 22formed in a transverse manner on a rack 24. As shown most clearly inFIG. 3, the teeth 22 extend in a nominally axial direction along thesurface of the rack 24. As is known in the art, input shaft 29 of therotary control valve assembly 18 is connected to a steering wheel (notshown) to enable steering of a host vehicle.

The rack 24 is mounted for reciprocal movement along an axis oftranslation "A" in an elongated cavity 26 of the housing 10. Rotationalmovement of the pinion gear 20 by the steering wheel and rotary controlvalve assembly 18 will cause reciprocal translation of the rack 24 alongthe axis of translation "A". As is known in the art, the rack 24 isconnected to dirigible wheels (also not shown) to steer the vehicle.

As shown in FIG. 1, a cylindrical sleeve 30 is formed on one side of thecylinder 14 of the housing. The cylindrical sleeve 30 includes athreaded aperture 32 for accepting an improved yoke assembly 34comprised in a preferred embodiment of the present invention. Thethreaded aperture 32 extends in a substantially orthogonal directionwith reference to the axis of translation "A" of the rack 24.

The improved yoke assembly 34 includes a bearing disc 36, an elastomericO-ring member 38 and an adjuster plug 40. When the improved yokeassembly 34 is assembled within the cylindrical sleeve 30, the bearingdisc 36 is biased against the rack 24 by compression of the O-ringmember 38 as is depicted more clearly in FIGS. 2 and 3.

As particularly shown in FIG. 2, one side of the bearing disk 36 has acurvilinear slot 42 defining a pair of arms 44. The slot 42 includes acutaway center portion 46 extending between a pair of elongated bearingsurfaces 48. The bearing surfaces 48 are spaced apart to guide the rack24 during movement thereof. The bearing disc 36 has a circumferentialouter surface 50 having a diameter less than the threaded aperture 32 ofthe cylindrical sleeve 30. The diametral operating clearance so obtainedprecludes the possibility of contact between the bearing disc 36 and thethreaded aperture 32 and eliminates any possibility of rattle from thatsource.

The other side of the bearing disc 36 has an inner angular contactgroove 52 and the juxtaposed side of the adjuster plug 40 has an outerangular contact groove 54. During assembly, the O-ring member 38 iscompressed between angular contact grooves 52 and 54 to provide abiasing force that urges the bearing disc 36 into contact with the rack24. Except for the lubrication wedge described below, the interfacebetween the bearing surfaces 48 and the rack 24 provides lateral,radial, pitch and roll constraints for the bearing disc with respect tothe axis of translation "A". Lateral positioning of both the bearingdisc 36 and the rack 24, as well as the remaining axial and yawconstraints for the bearing disc 36, are provided by the compressedO-ring member 38 in a somewhat compliant manner with respect to thethreaded aperture 32.

As a consequence of its axially directed compression between the angularcontact grooves 52 and 54, the O-ring member 38 also provides nominalpitch and yaw constraints upon the bearing disc 36 which are conicallydirected toward an apex 56. The actual location of the apex 56 isdetermined by the relative final locations of the lines of force throughthe angular contact grooves 52 and 54. In any case, the pitch constraintis directed about the apex 56 which is well within the rack 24 and thusphysically remote from the bearing disc 36. Upon initial translationalmotion of the rack 24, the bearing disc 36 begins to move along with therack 24. This tends to decompress leading edge portion 58 of the O-ringmember 38 (i.e., that portion under the leading edge 60 of the bearingdisc) and further compress trailing edge portion 62 of the O-ring member38 (i.e., that portion under the trailing edge 64 of the bearing disc).The end result is a contra-pitch rotation of the bearing disc 36 aboutthe apex 56 so as to form a lubrication wedge between it and the rack24. The kinematic design of the improved yoke assembly 34 permits theaxis of the bearing surfaces 48 of the bearing disc 36 to be in precisealignment with the rack 24 and maintain a lubrication wedge therebetweenwhich enables smooth movement of the rack 24.

During assembly, the adjuster plug 40 is threadably inserted intothreaded aperture 32 and rotatably driven until surface 66 thereofcontacts convex surface 68 of the bearing disc 36. Then the adjusterplug 40 is rotationally backed off a minimal predetermined distance,such as 10°, in order to permit some movement of the bearing disc 36 andrack 24. An internal lock nut 70 is then tightened against the adjusterplug 40 to maintain its position.

The minimal predetermined distance of 10° is significantly less thanthat normally encountered when assembling yoke assemblies of the priorart. This is enabled by the extra degree of freedom provided by theimproved yoke assembly 34 whereby the tightening of the adjuster plug 40against the bearing disc 36 can be accomplished in a more precisemanner. The result is tighter control of the operating clearance betweenthe adjuster plug 40 and bearing disc 36. This is important inminimizing rattle because it results in minimal possible separationbetween the pinion gear 20 and rack 24 as a consequence of dissimilardirigible wheel impacts. This, in turn, minimizes the maximum closurevelocity therebetween which minimizes any audible noise associated withclosure.

In practice it has been found that while the improved yoke assembly 34does provide for smooth, rattle-free movement of the rack 24, thehelically formed teeth 28 on the pinion gear 20 tend to initially drivethe rack 24 laterally. This, in turn, may cause the steering apparatusto exhibit a lack of on-center crispness. This is due a lack of initialtranslational motion of the rack 24 during the period when it is movinglaterally.

Therefore, as shown in FIGS. 4 and 5, an improved yoke assembly 72 ispresented wherein laterally disposed elastomeric members 74a and 74b areutilized to markedly increase yaw stiffness of bearing disc 76. Thelaterally disposed elastomeric members 74a and 74b are respectivelycaptured between lateral grooves 78a and 78b formed in sides 80a and 80bof the bearing disc 76, and respectively juxtaposed axially directedgrooves 82a and 82b formed within bore 84. In order to ease assembly,the lateral grooves 78a and 78b comprise lead-in tapers 86 so thatlateral compression of the laterally disposed elastomeric members 74aand 74b occurs gradually as a function of the axial assembly of thebearing disc 76.

In addition, the O-ring 38 described above (i.e., with reference to yokeassembly 34) is replaced with an elastomeric member 88 formed directlywithin adjuster plug 90. This eliminates handling a separate elastomericmember during assembly. In this case, elastomeric member 88 is formedwithin a nominally outer angular contact region 92 of the adjuster plug90. In so doing, the resulting conically directed pitch constraint isdirected toward apex 56 in a manner similar to that described above withreference to the improved yoke assembly 34.

Shown in FIGS. 6, 7 and 8 is an improved yoke assembly 94 wherein bothof the above described types of elastomeric members are formed in asecond operation directly within bearing disc 96 to form a compositeyoke member 98. This eliminates handling separate elastomeric membersduring assembly. In this case the bearing disc 96 is formed withmechanically interlocking shapes comprising passages 100a and 100b, andpocket regions 102. Then, in the second forming operation, elastomericmember 104 comprising laterally disposed protrusions 106a and 106b, andoutwardly directed axial rib 108, is formed within bearing disc 96 as isbest shown in FIG. 8.

Because the laterally disposed protrusions 106a and 106b aremechanically located with reference to the bearing disc 96, nojuxtaposed axially directed grooves, such as axially directed grooves82a and 82b, are required within bore 110. Instead, bearing disc 96 andbore 110 are formed in a conical manner so that compression of thelaterally disposed protrusions 106a and 106b occurs as a function of theaxial assembly of the composite yoke member 98. Similarly, pitchconstraints are directed toward apex 56 via compression of outwardlydirected axial rib 108 by outer angular contact groove 54 of adjusterplug 40.

In either of the improved yoke assemblies 72 or 94, respective laterallydisposed elastomeric members 74a and 74b, or laterally disposedprotrusions 106a and 106b, provide a substantial increase in yawstiffness for either of the bearing discs 76 or 96. Thus, the helicallyformed teeth 28 on the pinion gear 20 are substantially precluded fromdriving the rack 24 laterally. This, in turn, substantially enhanceson-center crispness.

In any of the improved yoke assemblies 34, 72 or 94, all of thenecessary constraints are elastomerically provided. Thus, the bearingdiscs 36, 76 or 96 are not required to be slidingly mounted in a bore inthe housing. And, there is no possibility of rattle occurring viacontact between the respective bearing disc and such a housing bore. Inaddition, because all of the constraints are elastomerically provided,engagement of the helically formed teeth 28 of the pinion gear 20 andthe teeth 22 of the rack 24 is maintained in a less abrupt manner.Should physical separation therebetween result from a dissimilar impacton the dirigible wheels, re-engagement is softer and somewhat damped. Inthis way, rattle due to gear re-engagement is minimized as well.

While the present invention has been described in connection with thepreferred embodiments of the various figures, it is also understood thatother similar embodiments may be used or modifications or additions maybe made to the described embodiments for performing the same function ofthe present invention without deviating therefrom. For instance, thepreferred embodiment could be implemented by directly forming acircumferential elastomeric element in either of the bearing disc 36 oradjuster plug 40 in the manner of elastomeric member 88 formed withinadjuster plug 90 and comprised in the improved yoke assembly 72.Therefore, the present invention should not be limited to any singleembodiment but, rather, construed in breadth and scope in accordancewith the recitation of the appended claims.

I claim:
 1. An apparatus for mounting a rack and pinion in meshingengagement, said rack movable on an axis of translation within ahousing, said housing having a bore formed on an adjustment axis whichis nominally orthogonal and intersects said axis of translation, saidapparatus comprising:a plug member mounted within said bore; a bearingdisc member compliantly mounted in said bore, said disc member having anominally cylindrical surface formed in a top portion and spaced apartfrom a lower surface, said cylindrical surface formed to support saidrack, said disc member having a peripheral surface extending from saidlower surface to said top portion, said peripheral surface being spacedinwardly from an inner surface of said bore such that said disc memberis movable from alignment with said adjustment axis; first means forbiasing mounted between said lower surface of said bearing disc memberand said plug; and second means for biasing having a pair of resilientportions disposed between said bearing disc member and said bore 180°apart on an axis extending through said cylindrical surface andorthogonal to said adjustment axis whereby said disc member isresiliently supported in said bore against yaw to resist displacement ofthe rack in a lateral direction.
 2. The apparatus of claim 1, havingsaid first biasing means formed of elastomeric material and having saidadjuster plug member and said lower surface of said bearing disc memberformed with means for receiving said first biasing means.
 3. Theapparatus of claim 1 having said second compliantly biasing means formedof elastomeric material and having said bore of said housing and saidbearing disc member formed with means for receiving said compliantlybiasing means.
 4. The apparatus of claim 1 having said first compliantlybiasing means and said second compliantly biasing means formed ofelastomeric material positioned within said bearing disc member.
 5. Theapparatus of claim 4 wherein said bearing disc member comprisesmechanically interlocking shapes and said elastomeric material is formedwithin said mechanically interlocking shapes of said bearing discmember.
 6. The apparatus of claim 1, wherein said first and second 2biasing means comprises a unitarily formed elastomeric member.
 7. Theapparatus of claim 1, wherein said first biasing means comprises anO-ring.
 8. The apparatus of claim 1, wherein said second biasing meanscomprises a pair of elastomeric pads.